When air pollutants are emitted to the atmosphere, they diffuse and move with the air current which makes it difficult to treat them, and the cost of treating them may considerably vary depending on the type of treatment method. Among such air pollutants, because volatile organic compounds (VOCs) are not completely removed using typical air purifiers, it is important that the type of pollutant be exactly checked and that the method adapted to remove them be selected.
Techniques for removing VOCs as above use the methods of adsorption, absorption, condensation, membrane separation and so on to recover the generated VOCs. Among these, the adsorption method for recovering VOCs using an adsorbent such as activated carbon or zeolite is widely utilized because activated carbon has a large surface area and so results in high adsorption capability, but is disadvantageous because the activated carbon is ignitable and it is difficult to regenerate and the humidity should also be adjusted (<50% RH) before processing. For this reason, hydrophobic zeolite having a large surface area, thermal stability and no need to control the humidity is employed as an effective adsorbent. This method has a low installation cost and thus is mainly applied to filters but the maintenance cost is high because of the short lifetime and frequent replacement cycles. In addition, techniques for removing organic compounds from air may include thermal incineration, catalytic incineration, UV-oxidation, biofiltration, etc. The thermal incineration method is used to directly incinerate organic compounds present in air at high temperature (700˜1100° C.) so as to remove them, and thus may treat a large amount of organic compounds in air. However, in the case where the load variation is severe or the concentration is low and the flow rate is low, the economic benefits may be negated. Also, in the case where poorly decomposable VOCs are present in exhaust gas, the combustion temperature may increase and thus relatively high operating cost is required, and furthermore the reaction temperature is high and thus there is a concern for generating secondary air pollutants such as NOx (Thermal NOx) via the oxidation of nitrogen in air upon high-temperature combustion. Moreover, because the system is comparatively large, a large mounting space is required, making it difficult to add equipment. Also, the catalytic oxidation method of removing VOCs is regarded as a very effective technique for converting harmful air pollutants into harmless materials, as is the thermal incineration method, and thorough research and development into ideal catalyst systems is ongoing. Such methods are advantageous because secondary pollutants such as nitrogen compounds are not generated, and the application places thereof have been recently increasing and thus thorough research and development into ideal catalyst systems is also ongoing.
In accordance with the catalytic incineration method, organic compounds present in air generated from a stationary source are combusted and removed using a catalyst. Compared to the high-temperature combustion method, harmful air pollutants may be effectively removed at a much lower reaction temperature, and furthermore, because the reaction temperature is low, the operating cost is profitably low, and almost no NOx is generated, and also the system is simple, making it easy to add equipment.
As an example of a system for removing organic compounds from air using adsorption/catalytic oxidation, U.S. Pat. No. 7,074,260 discloses a filter using carbon nanotubes.
This patent pertains to a filter comprising carbon nanotubes having one or more kinds of metal nanoparticles fixed thereto, wherein the fixing of the metal nanoparticles to the carbon nanotubes may be performed by holing pure graphite bars using an electric discharge process or a laser vapor-deposition process, filling the holes of the graphite bars with metal powder and then carrying out synthesis, or by using metal-mixed graphite as a target, thus obtaining functional carbon nanotubes having metal particles fixed thereto. However, this patent is problematic because it is difficult to constantly adjust the size of the metal particles and uniformly disperse the metal particles.
In addition, as an example of a system for removing organic compounds from air using adsorption/catalytic incineration, Korean Patent Publication No. 10-2004-0012364 discloses a VOC removal system using adsorption/catalytic oxidation to treat VOCs present in low concentration.
More specifically, Korean Patent Publication No. 10-2004-0012364 proposed a VOC removal system wherein the hydrophobic zeolite adsorbent and the VOC oxidation catalyst are embodied in a single system and thus the VOCs are concentrated on the hydrophobic zeolite adsorbent layer, heated and desorbed, thereby decomposing the desorbed VOCs in the oxidation catalyst layer to remove them. However, this VOC removal system requires additional two heating units for heating not only the adsorbent layer to desorb the adsorbed VOCs from the hydrophobic zeolite adsorbent layer but also the catalyst layer to decompose the desorbed VOCs using the oxidation catalyst.
In particular, because the combination of an adsorption method and a catalytic incineration method, which adsorbs the organic compounds in air and incinerates them using a catalyst, has the advantages of both the adsorption method and the catalytic incineration method, there is a need to develop an efficient adsorption/catalytic system and a device for removing organic compounds from air using the same.